Preventing corrosion during the pipeline transportation of coal slurries

ABSTRACT

A method for rendering a coal-water slurry non-corrosive to a pipeline during pipeline transportation of the slurry by admixing therewith, and maintaining therein, a hexavalent chromate corrosion inhibitor in combination with a minor amount of less than 1000 ppm of an inhibitor saving additive selected from the group consisting of gelatin and a reaction product of an alkyl phenol and an alkylene oxide.

United States Patent [1 1 Titus et a1.

[ PREVENTING CORROSION DURING THE PIPELINE TRANSPORTATION OF COAL SLURRIES [75] Inventors: Paul E. Titus; Joseph S. Di

Gregorio, both of Houston, Tex.

[73] Assignee: Shell Oil Company, New York, NY.

[22] Filed: July 28, 1971 [21] Appl. No.: 166,851

[56] References Cited UNITED STATES PATENTS 2,128,913 9/1938 Burk 302/66 X 2,346,151 4/1944 Burk et a1. 44/1 R [451 Feb. 11, 1975 Primary Examiner-Barry S. Richman [57] ABSTRACT A method for rendering a coal-water slurry noncorrosive to a pipeline during pipeline transportation of the slurry by admixing therewith, and maintaining therein, a hexavalent chromate corrosion inhibitor in combination with a minor amount of less than 1000 ppm of an inhibitor saving additive selected from the group consisting of gelatin and a reaction product of an alkyl phenol and an alkylene oxide.

3 Claims, 1 Drawing Figure PATENTED FEB] 1 i975 COAL GELAT/NE COAL ELAPSED TIME (HOURS) PREVENTING CORROSION DURING THE PIPELINE TRANSPORTATION OF COAL SLURRIES BACKGROUND OF THE INVENTION The transportation of coal in slurry form through pipelines is well known in the art as evidenced by reference to articles by G. A. Orrok et a1, Power, Nov. 1, 1921, pages 699-700; C. L. Barthauer et a1, Canadian Mining and Metallurgical Bulletin, December, 1970, pages 1373-1377, and Materials Protection, September, 1963, pages 26-34, or US. Pat. Nos. 2,128,913, 2,346,151, 2,791,472 and 3,129,164.

Although pipeline transportation of coal slurries is becoming more and more attractive over other means of coal transportation in non-slurry form such as by railroad cars, tankers, trucks, such non-slurry form of coal transportation is becoming more and more unattractive because of limited handling capacity, high handling costs as well as other economic factors. Pipeline transportation of coal in slurry form because of its ease of handling and unlimited capacity is, therefore, becoming more attractive over conventional means of transportation mentioned since this form of transportation coal is a more convenient and economical, particularly where the coal is to be transported over great distances. However, a number of problems are presented when pipeline transporting coal slurries and there are the tendency of coal slurries to cause corrosion and plugging during transportation and particularly on shutdown resulting in re-start difficulties.

In the above-cited references, Barthauer indicates that corrosion can be essentially alleviated in pipelines transporting coal-water slurries by maintaining in such slurries a small amount of chromate ion containing hexavalent chromium in concentration above 12 ppm and maintaining said slurries at pH of above 6. These slurries comprise 35-55 percent of coal particles of Tyler size of-6-28 mesh of which less than percent are less than 14 Tyler mesh. In order to maintain the chromate concentration within desired limits, because it becomes depleted due to its tendency to become adsorbed on or react with the surface of the coal particles, chromate is injected in increments along the path of the pipeline to keep the chromate at a desired high level. Since the chromate is lost within short periods of time, because of its tendency to be adsorbed on the coal, its effectiveness as a corrosion inhibitor is limited.

An object of the present invention is to prepare a corrosion resistant coal slurry.

Still another object of the present invention is to prepare a non-clogging or non-plugging, corrosion resistant coal slurry in a liquid carrier.

Still another object of the present invention is to prepare a non-clogging or non-plugging, corrosion resistant coal-water slurry for pipeline transportation.

Still another object of the present invention is to pipeline transport a coal slurry which is non-clogging and non-plugging and does not cause corrosion of the interior of the pipeline or equipment handling said slurry.

Still another object of the present invention is to pipeline transport a coal-water slurry which is resistant toward corrosion and plugging and can be readily restarted after pipeline shutdown if and when required.

Still another object of the present invention is to transport non-corrosive non-clogging coal slurries over great distances under conditions of reduced pumping and handling costs.

Other objects will be apparent from the following description.

SUMMARY OF THE INVENTION The above and other objects of the present invention are achieved by preparing a 10-60 percent slurry coal in particle form of from about 30 to less than 325 mesh (U.S. sieve or Tyler mesh size) of which at least 15 percent or more of said coal particles are 325 mesh and the remainder of said slurry (-40%) being a liquid carrier preferably an aqueous liquid to which total slurry is added from 10-1000 ppm each ofa hexavalent chromate compound and a high coal adsorptive additive which is essentially a water-soluble polarcontaining compound having a high affinity for coal adsorption which is greater than that of the chromate compound. Optionally, the polar-containing compound, e.g., gelatin as well as other improving agents such as friction reducers, viscosity controlling agents can be incorporated into coal slurry compositions containing the chromate during the preparation of the slurry or after the slurry has been prepared and injected into the pipeline and these additives can be injected simultaneously or sequentially; and if this is done, the improving agent should be added first.

In preparing non-corrosive coal slurries of the present invention coal particles of from l4+30 to 325 mesh in an amount of from about 10 percent to about 60 percent or higher are slurried into a liquid carrier such as a liquid aqueous medium and during or after, simultaneously or sequentially, from about 10 to 1000 ppm each of a chromate compound and a water-soluble polar-containing compound as defined is addedto the slurry and admixed to form a homogeneous mass. The operation can be conducted in an inert environment, at ambient or elevated temperature, depending on the condition of the liquid carrier. The coal slurry can then be injected into a pipeline for transportation over great distances without causing corrosion, plugging and on shutdown, the slurry can be re-started without any difficulties. An option is to prepare the coal slurry, inject it into a pipeline, and while the slurry is being pumped to a terminal station injecting, simultaneously, sequentially and/or in increments, the chromate and polarcontaining compound having high affinity for coal adsorption.

Coal slurries made from coal particles in the size range of the present invention resist attrition while being pipeline transported. The coal particles from different fields useful in making slurries of the present invention are illustrated in Tables 1 and II, at varying velocities of transportation over large distances.

TABLE I Weight Percent Coal in Each Size Range Concentration =33% by volume Velocity 6 ft/sec TABLE I-Continued Weight Percent Coal in Each Size Range Concentration 33% by volume Velocity =6 ft/sec WEIGHT PERCENT COAL IN EACH SIZE RANGE Tyler Mesh The chromates useful as corrosion inhibitors in coal slurry compositions of the present invention include hexavalent chromates, preferably the water-soluble chromates such as alkali metal chromates, e.g., Na and- /or K chromates (Na CrO and/or K CrO The water-soluble polar-containing compound, having high affinity for adsorption on coal particles used in conjunction with the chromate and which prevents the chromate from being adsorbed on the coal but rather onto the pipeline wall thereby rendering the pipeline resistant to erosion and corrosion, include: watersoluble oxygen-containing materials such as reaction products of alkylene oxide, e.g., ethylene and/or propylene oxides and hydroxyl-containing organic compounds such as alkyl phenols, naphthols, acid phosphates; hydroxylamines, e.g., ethanolamines, polyhydroxy polyamines; polysaccharides, sugars and their derivatives, gelatin, polymers of unsaturated acids and their derivatives, e.g., polymethacrylate; polyacrylamide; hydrolyzed polyacrylamide (Separan) of which preferred are gelatin and reaction products of ethylene oxide and C, alkyl phenol, e.g., Triton X-100, Triton X-45, Igepal CO-530 and/or 990 and mixtures thereof.

By the combination of chromate and water-soluble coal adsorptive additive or compound as described, lesser amounts of chromate are required to inhibit corrosion, maximum corrosion inhibiting effectiveness is achieved.

PREFERRED EMBODIMENT OF THE INVENTION To illustrate the novel features of the present invention, tests were carried out with a 50 percent volume 'water slurry of dry-ground Crowsnest coal (Alberta,

Canada) which showed that dissolved oxygen was removed from the aqueous phase in about 8 to 10 hours (FIG. 1, lower curve). The particle size distribution of the coal sample tested is shown in Table III.

The pH of the Crowsnest coal/water slurry did not vary with time, but remained at about 5.5 to 6.0 with distilled water as the carrier, indicating that no additional acidic components were extracted from the coal.

The depletion of the dissolved oxygen is apparently caused by adsorption. This was shown by the addition of a small amount of gelatin to the coal/water slurry.

Gelatin consists of large organic molecules that cover up active adsorption sites on the coal surface. As shown by the upper curve in FIG. 1, the addition of 10 ppm of gelatin to the coal/water slurry retarded the oxygen depletion previously observed.

Screening of corrosion inhibitors was carried out using a bottle rotating test. Description of test conditions is shown in Table IV. The results of the tests are shown in Table V. All slurries were made with distilled water. Corrosion rates experienced with uninhibited slurries, and in water alone, are shown in Table VI, for purposes of comparison.

TABLE III Particle Size Distribution of Crowsnest Coal (Canada) %w Retained Size, Oxygen Depletion Corrosion Inhibitor U.S. Sieve Test Sample (1) Test Sample (2) 30 5 12 5O l5 18 15 20 200 20 31 325 l0 11 325 35 8 TABLE IV Corrosion Inhibitor Screening Test Conditions 250 ml magnesia bottles in bottle rotating apparatus. ml slurry in each bottle. Slurry consists of 50%v coal as in Table I plus distilled water.

0.03 X 0.5 X 6-inch specimens of carbon steel, sand blasted surface.

Room temperature (70-75F), atmospheric pressure, air atmosphere at start of test. Bottles rotated end-overend at 8 rpm. Test duration equals 7 days.

TABLE V Corrosion Rates of Various Coal/Water Slurries Slurry contained 50%v coal of particle size distribution shown in Table 111, Sample 1.

Coal sample had particle size distribution as shown in Table 111 Sample 1. Basis total slurry.

TABLE VI Corrosion of Steel by Various Coal/Water Slurries Conditions as shown in Table Coal Corrosion Rate Samples(a) Water pH mils/year (b) Canadian water alone .0 5.4 Distilled water alone 6.3 2 Canadian 6.0 7.5 2 Distilled 5.7 7.5

TABLE Vl-Contin ued Corrosion of Steel by Various Coal/Water Slurries Conditions as shown in Table (a) Numbers refer to samples described in Table II]. (b) From weight loss and exposure time No localized attack noted.

From the tests shown in Tables lll-Vl, it is evident that the presence of large organic molecules, e.g., Triton X-l or gelatin, is beneficial in enhancing the corrosion inhibition of chromate salts.

Comparable results can be obtained when a 50--50 coal-water slurry containing l2.5 ppm chromate (K CrO and 5 ppm Triton X-100 after 500 miles of transporting said slurry through the pipeline.

An added feature of coal slurry compositions of the present invention containing chromates and polarcontaining adsorbents is that attrition of the coal particles in the slurry is essentially inhibited, thereby reducing the problem of plugging of the pipeline and facilitating restart whenever necessary.

The foregoing description of the invention is merely intended to by explanatory thereof. Various changes in the details of the described method may be made within the scope of the appended claims without departing from the spirit of the invention.

We claim:

1. in a method for rendering a coal-water slurry noncorrosive to a pipeline by admixture therewith of a hexavalent chromate corrosion inhibitor, the improvement comprising maintaining the coal-water slurry noncorrosive during pipeline transportation thereof by addition thereto ofa minor amount of less than 1000 ppm of an inhibitor saving additive selected from the group consisting of gelatin and a reaction product of an alkyl phenol and an alkylene oxide.

2. In a method for rendering a coal-water slurry noncorrosive to a pipeline by admixture therewith of a hexavalent chromate corrosion inhibitor, the improvement comprising maintaining the coal-water slurry noncorrosive during pipeline transportation thereof by addition thereto ofa minor amount of less than 1000 ppm of isooctyl phenoxy polyethoxy ethanol as an inhibitor saving additive.

3. In a method for rendering a coal-water slurry noncorrosive to a pipeline by admixture therewith of a hexavalent chromate corrosion inhibitor, the improvement comprising maintaining the coal-water slurry noncorrosive during pipeline transportation thereof by addition thereto of 10 to 1000 ppm of an inhibitor saving additive selected from the group consisting of gelatin and a reaction product of an alkyl phenol and an alkyl- 

1. IN A METHOD FOR RENDERING A COAL-WATER SLURRY NONCORROSIVE TO A PIPELINE BY ADMIXTURE THEREWITH OF A HEXAVALENT CHROMATE CORROSION INHIBITOR, THE IMPROVEMENT COMPRISING MAINTAINING THE COAL-WATER SLURRY NON-CORROSIVE DURING PIPELINE TRANSPORTATION THEREOF BY ADDITION THERETO OF A MINOR AMOUNT OF LESS THAN 1000 PPM OF AN INHIBITOR SAVING ADDITIVE SELECTED FROM THEGROUP CONSISTING OF GELATIN AND A REACTION PRODUCT OF AN ALKYL PHENOL AND AN ALKYLENE OXIDE.
 2. In a method for rendering a coal-water slurry non-corrosive to a pipeline by admixture therewith of a hexavalent chromate corrosion inhibitor, the improvement comprising maintaining the coal-water slurry non-corrosive during pipeline transportation thereof by addition thereto of a minor amount of less than 1000 ppm of isooctyl phenoxy polyethoxy ethanol as an inhibitor saving additive.
 3. In a method for rendering a coal-water slurry non-corrosive to a pipeline by admixture therewith of a hexavalent chromate corrosion inhibitor, the improvement comprising maintaining the coal-water slurry non-corrosive during pipeline transportation thereof by addition thereto of 10 to 1000 ppm of an inhibitor saving addiTive selected from the group consisting of gelatin and a reaction product of an alkyl phenol and an alkylene oxide. 